I agree, because (potentially) there are two main different ways the basket resonance can be invoked. This other way happens when the pressure in the box moves the baffles. Magnet mounting ensures the basket resonance can get between this.
Box pressure is really only an issue at the lowest frequencies, which we do hop 2 BIG woofers will give you. It has a special name. Ballooning.
dave
dave
I really should expand that to include any way the baffles move. Although it gets complicated... if the magnets are held at a place that represents the cabinet 'ground point', then any baffle movement relative to that will simply join with the basket resonance.
Yes, you can use a much lighter construction.
It is easy to calculate the pressures involved p=t/v and the delta v is really small. Do the math if you like. The problem is that flat surfaces are not the best for pressure vessels. So for a really light weight enclosures, you need curves. Compound curves preferably. Just make sure that the reaction forces from cone acceleration are not fed through the enclosure by directly coupling the drivers.
It is easy to calculate the pressures involved p=t/v and the delta v is really small. Do the math if you like. The problem is that flat surfaces are not the best for pressure vessels. So for a really light weight enclosures, you need curves. Compound curves preferably. Just make sure that the reaction forces from cone acceleration are not fed through the enclosure by directly coupling the drivers.
Such a project. Push-Push loading, Push-Pull isobarik drivers. 4 12” Foster drivers / tube, 2 tubes. Pipe cut to the perfect length.
Free for anyone who can pick it up and finish it. That is a LR 4th order active XO (ideally it needs some grounding tweaks at a minimum)
dave
If you directly mount two magnets back to back, it's a ridged, solid connection, if you don't, the chassis/enclosure will act like springs and you'll end up with a tunning fork - this effect is so pronounced that when I connected to opposing magnates together with a 20mm dia, 200mm long steel bar (with threaded studding going through the whole lot) I ended up with a "zingy" sound, when I removed the steel bar and used the enclosure to connect them it still remained, only cured by adding baby-belle red cheese wax to the gap between the pressed steel chassis and the magnet, which damped the vibration; in this application I was using the drivers full range, perhaps if the were just used for bass the resonance would be too far away to cause a problem. On my packing case speakers, I used a little bit of foam between the magnet and an internal deflector to dampen chassis/enclosure vibration, but without testing a with and without, it's difficult to access how effective it is. Car speakers are often derided, but the coaxial ones do have the advantage of a hole through the pole piece, that's handy for bolting the magnet to something.
Dave, that is just perfect. My first round speakers were made from 12 inch American PVC pipe. Which has walls much thicker than European drain pipe used for the same purposes. But even 4 mm walls are plenty to contain the pressures involved.
It all comes down to trade off's like everything, for me ply is hard to justify due to price here and for a sub box that's not portable MDF weight only matters only very rarely and a sack truck/hand trolley will fix that problem easy(KISS theory).
There's also a strong case for using chip board as its cheapest and much stiffer than MDF or even OSB if you can get it thick enough... that'll stir the pot!
There's also a strong case for using chip board as its cheapest and much stiffer than MDF or even OSB if you can get it thick enough... that'll stir the pot!
Used (braced) corrugated, cement cardboard (AKA 'papercrete' nowadays apparently) worked well for me in my early DIY days; my first BLH was a 1/4 scale corrugated cardboard Jensen from this March '52 drawing set.